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TMS320F28374S: CMPA and CMPB waveform complementary failure

Part Number: TMS320F28374S

When configuring three-level wave generation, CMPA and CMPB(complementary) configurations are used. It is found that the tube is always on (or off), there is an exception, and there is no corresponding complementary. Are there any analysis directions or suggestions?

See Figure 1 for specific configuration;

The actual measured waveform is shown in Figure 2;

Refer to figure 3 for normal waveform.

Figure 1 DSP configuration: 

Figure 2 abnormal waveform,4 channel are CMPA,3 channel are CMPB.

When channel 4 is always high, channel 3 should always be low, but some pulses appear, and the pulse width is the dead band setting time.

Figure 3 normal waveform 4 channel are CMPA,3 channel are CMPB.

  • Hi Delmore,

    Are you changing your duty cycle throughout your application? I see initially you configure CMPA to equal TBPRD. 

    What is the value of TBPRD that you are setting? If you apply a fixed duty cycle value (lets say 50%) do you see this issue occur?

    Could you pause your program when you see the output behave in a non-complementary fashion and check the state of all of the registers? This will help narrow down the issue.

    Best Regards,
    Marlyn

  • 1. TBPRD in the program is the fixed value: 6250;

    2. Set a fixed duty cycle, there will be no problem. The waveform is complementary up and down, which is OK;

    3. According to the non complementary method, the register configuration does not change with the complementary configuration. Register configuration is operated during initialization, and only CMPA is updated during operation.

  • Hi Delmore, 

    Thank you for providing further information. Do you know what value of CMPA causes the outputs to be non-complementary? 

    Best Regards,

    Marlyn